Choosing Vinyl Windows

Vinyl windows are inexpensive, durable, and never need paint

Vinyl windows first showed up in the U.S. in the 1960s, but
they didn't gain widespread acceptance until the 1980s.
Recently, vinyl overtook wood as the most common window
material in the U.S. Vinyl windows now account for about 40% of
total window sales and around 60% of the replacement
market.

Some products combine wood and vinyl, but all-vinyl windows
have sash and frames made from hollow pieces of polyvinyl
chloride (PVC). Glazing and hardware vary by brand and model
but are comparable to what you'll find on wood and metal
units.

The main selling points for vinyl windows are price and
durability. All things being equal, vinyl windows cost about a
third less than comparable wood or clad-wood units. The
installed cost is even lower because there's no need to paint
the window after it's nailed to the building. Eliminating
painting can also reduce overhead by allowing you to finish the
job sooner.

Besides never needing paint, vinyl windows won't rot, and
vinyl doesn't swell or warp when it gets wet. As with any
product, quality varies by brand and model, however. To
understand the differences, it helps to know how vinyl windows
are made.

Making Vinyl Windows

Vinyl window parts start out as powdered PVC resin. The resin
is mixed with additives to form a vinyl compound, which is
melted and forced through dies. What comes out is a hollow
extrusion that's divided into separate chambers by a series of
internal walls.

The extrusions are then cut into 16- or 20-foot lengths and
shipped to the fabricator. In most cases, fabricators outsource
extrusions, but a few of the larger manufacturers produce their
own.

At the fabrication plant, extrusions for sash and frames are
cut to length, mitered, and joined at the corners. The frames
on low-end windows are sometimes joined with screws. But on
most windows, frames and sash are joined by fusion welding,
which involves melting the ends and pressing them together.
This produces strong corners that are airtight and watertight.
Assembly is completed by installing glass, weatherstripping,
and hardware.

Additives Make the
Difference

Most vinyl compounds are 80% PVC resin and 20% additives. But
it's the additives that determine the physical properties of
the material. The compounds used in early windows weathered
poorly, which led to problems like brittleness, yellowing, and
surface pitting. As compounds improved, those problems became
less common. Today's windows contain UV-stabilizers to resist
the sun and modifiers to enhance toughness and
flexibility.

Many companies that make vinyl windows also make vinyl doors.
It's easier to gang doors and windows that come from the same
manufacturer.

Dimensional stability. Excessive thermal expansion was
a problem with earlier windows. As the temperature changed,
vinyl parts expanded and contracted more than surrounding
materials. This differential movement led to broken glass
seals, poorly fitting sash, and failed caulk joints between
frame and exterior trim. Modern compounds are much more stable,
but vinyl still moves more than wood, metal, or glass.

Vinyl movement today is unlikely to affect the window, but
it's a reason to be careful about the joints between windows
and exterior walls. Special vigilance is required with stucco
or any other installation that relies on caulk to keep the
water out. Don't assume that the methods you use to install
wood or metal windows will work equally well for vinyl. Ask the
window manufacturer and the vendor what they suggest. It might
mean using backer rod and high-performance sealant instead of
cheap latex caulk. But that's a small price to pay for an
installation that doesn't leak.

Strength and Durability

The walls of vinyl extrusions are typically 1/16 to
3/32 inch thick. Sounds thin, but the interior walls
reinforce the exterior in much the way that chords reinforce a
roof truss. Another benefit of this chambering is decreased
thermal conductivity, because the air pockets act as
insulation. Before buying windows, make sure you see a picture
or, better yet, samples of the extrusions. In general, the
thicker the vinyl and the more chambers in the extrusion, the
better.

Like most vinyl windows for new
construction, this one comes with an integral nailing flange.
Some manufacturers offer windows with an optional attached
vinyl brickmolding.

Vinyl is a thermoplastic, meaning that when it gets hot
enough, it will start to melt. In hot, sunny climates it's not
unusual for surface temperatures to reach 160 degrees. In
theory, that poses a problem for vinyl windows. The concern is
that the vinyl will soften enough to deform under the weight of
the glass. But in practice, the air-pocket insulation keeps the
inner walls cool, allowing them to maintain their
strength.

Reinforcing. Windows should be strong enough to withstand
heavy wind loads, attempts at forced entry, and normal wear and
tear. Even though extrusions may be strong enough to stand up
to those things on their own, manufacturers sometimes reinforce
them by putting steel or aluminum stiffeners in the
chambers.

Vinyl parts have multiple inner chambers
and, as is the case with these sash, can be reinforced with
metal stiffeners. This particular window is a replacement unit,
which is why it has no nailing flange.
The bigger the window, the more likely it is to be
reinforced. Metal is frequently used in the perimeter of large
sash and in the stiles and rails of vinyl doors. It's also
placed in strategic areas in windows of all sizes. Typical
locations include meeting rails, sills, and the side jambs of
mulled units. It's worth asking when and where the manufacturer
reinforces windows. Some companies do a lot of reinforcing, and
others do almost none.

Shopping for Vinyl Windows

Window manufacturers come in all shapes and sizes. Some are
large national and regional companies that build with wood,
metal, and vinyl. Others are small to medium-size companies
that make only vinyl windows. There are lots of local window
shops. Some sell well-known brands, while others sell their own
private label. While it's possible to do small-scale
production, many companies outsource production to larger
manufacturers. One such manufacturer is Republic Windows &
Doors, which produces private-label windows for window shops
and for builders and remodelers looking for a way to
differentiate themselves in the marketplace.

Vinyl windows start out as 16- or
20-foot PVC extrusions. The pieces in this stack of frame parts
are about to be cut to length.

In most cases, the same kinds of windows are available in
vinyl as in wood. You can't get true-divided lites, but you can
get windows with grids sandwiched between the glass. Other
options include snap-in wood jamb extensions and channels for
drywall returns. Units are also available with vinyl brickmold
or J-channel to accept vinyl siding. One of the more unusual
products on the market is Polybau's tilt-pivot window. Common
in Europe, this type of window is seen in the U.S. rarely and
usually as a high-end mahogany unit.

Product offerings vary by region and company. Double-hungs are
especially popular in the eastern half of the country, while
sliders and replacement units are more popular in the West. One
thing to consider when choosing a brand of windows is the
breadth of the product line. In addition to windows, many
companies make hinged and sliding vinyl doors. Getting all the
windows and doors for a project from the same vendor is a plus.
The units will match and are more likely to show up at the same
time.

Replacement windows. Vinyl windows have been especially
popular as replacement windows because it's easy to get them in
custom sizes. Manufacturers have designed vinyl windows that
can be installed in or over the existing jamb, so there's no
need to remove or damage the existing trim. This lowers the
cost of replacement by reducing the time, mess, and labor that
go into the job.

In most cases, the replacement unit screws into the existing
opening and is caulked in place. You can also get replacements
with something called a stucco fin. The fin, which looks like a
wide, thin exterior casing, overlays the existing window and
laps onto the stucco. That allows you to replace windows
without patching stucco or repainting anything on the exterior
of the building.

Color. Although vinyl comes in every color of the
rainbow, most vinyl windows are either white or beige. A few
are brown or bronze. Because dark colors absorb more heat,
windows are usually light colored. Choices are limited because
of the need to standardize extrusions.

Sash and frame extrusions are cut to
length and mitered with automated chop saws.

The mitered ends of these frame parts
are being heated to the melting point in a fusion welding
machine. If you look closely, you can see that the ends have
started to curl from the heat.

Pneumatic clamps hold the melted ends of
extrusions together until they cool and harden into a single
piece.

There's no denying that from up close, vinyl windows look like
they're made from plastic. On the other hand, the color goes
all the way through the material, so scratches and dings are
hard to see. It is possible to paint vinyl, but you should
avoid painting vinyl windows because in most cases it will void
the warranty. Some companies offer windows with wood grain
interiors or interior surfaces that have been clad with real
wood veneer.

Quality Standards & Energy
Ratings

The American Architectural Manufacturers Association (AAMA)
sets minimum quality standards for vinyl windows. Manufacturers
submit sample windows for independent lab testing, which
includes testing corner welds for strength, testing the windows
against forced entry, and testing extrusions for strength,
impact resistance, color retention, and heat resistance. If the
windows pass, the manufacturer can put an AAMA sticker on that
type of window to verify that it and all its components meet
certain strength and durability standards.

Warranties. Many vinyl windows come with a lifetime
warranty on the sash and frame. In most cases, "lifetime" means
for as long as the current occupant owns the house.

Insulated glass units are usually warranted against seal
failure for 15 to 25 years. And hardware is normally covered
for 2 to 10 years. Those coverages are typical for windows that
go into single-family homes. Stricter terms apply to windows in
commercial and multifamily units. Be sure not to do anything to
void the warranty. Many companies void the warranty, for
example, if you install the window with expanding foam, because
it can exert enough pressure to deform the frame.

The fused corner joint of this sample sash is strong and
watertight. The finished joint would be completely invisible
were it not for the small amount of excess vinyl that remains
from the welding process.

Energy efficiency. All things being equal, vinyl
windows are as energy efficient as windows made from wood.
Vinyl is a good insulator and works with the air pockets to
slow the transfer of heat. Because windows are mostly glass,
minor differences in the U-values of different sash and frame
materials are not significant.

Glazing has a huge effect on the performance of any window.
The most efficient windows have gas-filled insulated glass
units with warm-edge spacers and low-e coatings. A variety of
configurations are available; the one you select should be
based on the local climate and sun exposure of the
building.

The simplest way to determine the efficiency of a window is to
look at the label. The better ones will have an Energy Star
label from the Department of Energy (DOE) and a label from the
National Fenestration Rating Council (NFRC).

Energy Star. The Energy Star label certifies that the
window meets minimum DOE standards for your climate. In some
areas, homeowners who install Energy Star windows are eligible
for tax credits or utility company rebates.

NFRC. The NFRC label contains test data for the size
and type of window you're buying. It shows the insulation
value, or U-factor of the window, along with an air-leakage
(AL) rating. The lower the numbers, the better. The label also
covers glazing and includes the solar heat gain coefficient
(SHGC) and visible transmittance (VT). SHGC measures how well
the glass blocks heat caused by sunlight; low numbers of it are
better as well. VT measures how much visible light passes
through the unit. Tinted glass has a lower VT than untinted
glass.

NFRC ratings are helpful, but you shouldn't use them to
compare different sizes or types of window. You can use them to
compare two vinyl casements or a vinyl casement with a wood
casement, for example, but not to compare double-hungs with
sliders or to compare units of greatly differing sizes.

David Frane is a finish carpenter and contributing
editor to The Journal of Light Construction. Special thanks to
Polybau for allowing us to photograph the production process at
its facility.